An overbearing entity in a specific industry or sphere of activity. A seemingly unbeatable presence always to be reckoned with; whose experience, influence, and skill threatens to defeat competitors with little effort.

In the software industry, Microsoft would be considered the 800-pound gorilla.
The New York Yankees or Manchester United might be considered the 800-pound gorillas of their respective sports.

“I can’t think of anybody who had more impact than Dr. Dobson,” on rousing evangelicals to the polls, Richard Viguerie, a GOP direct-mail guru, recently told U.S. News & World Report. “He was the 800-pound gorilla.”